Japanese Unexamined Patent Application Publication No. 8-5758 discloses one of known electronically controlled mechanical watches wherein hands fixed to a wheel train are precisely driven to indicate the time of day right by converting mechanical energy produced upon unwinding of a mainspring into electrical energy with a power generator, operating a rotation controller with the electrical energy, and then controlling a current value flowing through a coil of the power generator.
In operation of the above watch, the electrical energy produced from the power generator is once supplied to a smoothing capacitor, and the rotation controller is driven with power from the capacitor. However, because an AC electromotive force is always inputted to the capacitor in synch with the cycle of rotation of the power generator, it is not required to, for a long time, hold power for enabling the operation of the rotation controller which includes an IC and a quartz oscillator. Therefore, a capacitor having a comparatively small electrostatic capacity just enough to operate the IC and the quartz oscillator for a time as short as several seconds has been employed in the past.
The above electronically controlled mechanical watch is featured in that, because the hands are driven by using the mainspring as a power source, a motor is not required, thus resulting in the less number of parts and a lower cost. In addition, power generation is only needed to produce slight electrical energy necessary to operate an electronic circuit, and the watch can be operated with small input energy.
However, the above electronically controlled mechanical watch has problems as follows. When setting the hands right (or setting the watch to the correct time) by pulling out a crown, all of hour, minute and second hands have been usually stopped so that the watch can be set to the correct time. For stopping the hands, the wheel train is stopped and, to this end, the power generator is also stopped.
To continue driving of the IC while stopping the supply of the electromotive force from the power generator to the smoothing capacitor, therefore, charges accumulated in the capacitor are discharged to the IC side and the terminal voltage of the capacitor is lowered. As a result, the rotation controller is also brought into a stop.
Accordingly, when the driving of the power generator is restarted by pushing in the crown after setting the hands right, it takes a time to accumulate charges in the capacitor to such an extent that the terminal voltage of the capacitor reaches an IC driving start voltage (i.e., a voltage at which the IC can start driving). At the start of driving of the power generator, the power generator produces a small electromotive force when its rotational speed is slow, and a large electromotive force when its rotational speed is fast. This means that the rotational speed of the power generator must be quickly increased at the startup. However, because the power generator and the associated driving mechanism have their own inertia, it takes a time for the power generator to transit from a stopped state to an ordinary driving (rotating) state due to the inertia. Where an inertia plate is provided on a rotor of the power generator, particularly, the rotor gradually increases a rotational speed at the startup of the power generator. Accordingly, when the rotor starts rotation, a large torque is required and it takes a time until the rotational speed increases to a sufficient value. As a result, the amount of power produced by the power generator is small in an initial stage of the startup of the power generator, and charging takes a time until the terminal voltage of the capacitor reaches the IC driving start voltage. Stated otherwise, a problem has been experienced in that a certain period of time is needed from the start of driving of the power generator to the start of operation of the IC, and precise time control cannot be made during that period of time.
In view of the above problem, as disclosed in Japanese Unexamined Patent Application Publication No. 11-14768, the applicant has invented a method which can rotate a rotor at an increased speed and quickly increase the amount of generated power as soon as the startup, thereby shortening a time required for charging. According to this method, a driving lever is held in contact with a gear of the wheel train and is departed away from the gear with the operation of pushing in the crown after setting the hands right, so that the rotor is rotated by a mechanical rotating force imposed on the gear due to a frictional force produced upon the departing of the driving lever.
In the above invention, however, the driving lever applies a mechanical rotating force to the gear with a frictional force, thus resulting in a problem that it is difficult to efficiently apply the rotating force with stability. Such a problem is not limited to a power generator, but occurs likewise when a mechanical rotating force is applied to a motor gear with a frictional force using a driving lever. In other words, the above problem is in common to any cases where a driving lever is provided to impose a rotating force on a gear of mechanical energy transmitting means, such as a rotor or a train wheel for driving the rotor, in electromagnetic converters including power generators or motors.
A first object of the present invention is to provide a starter for an electromagnetic converter and a timepiece, which enable a mechanical rotating force to be efficiently applied to a rotor or mechanical energy transmitting means with stability.
Further, in the invention disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 11-14768, the mechanical rotating force applied by the driving lever needs to be set based on balance between a resilient force of an abutment portion coming into direct contact with the gear and a resilient force of a member for returning the abutment portion to its original position. This has raised a problem that a difficulty in setting of the rotating force makes it hard to apply a stable rotating force. In practice, if a return spring is too strong, a sufficient rotating torque cannot be applied because the spring causes the abutment lever to depart away from the gear before the startup. Conversely, if the return spring is too weak, the abutment lever is brought into contact with the gear upon an impact or the like.
A second object of the present invention is to provide a starter for an electromagnetic converter and a timepiece, which enable a mechanical rotating force to be applied to a rotor or mechanical energy transmitting means with higher stability.
Another problem in the case of applying a mechanical rotating force to a gear resides in efficiency.
More specifically, an appropriate rotational speed of the rotor is in the range of about 5–10 Hz, taking into account such conditions that the rotor can rotate with stability, and air resistance and viscosity resistance will not become too large. Also, from the standpoint of stability in rotation, an inertia disk is required as described above. The inertia disk is made of brass, for example, and its appropriate size is given by an outer diameter of about 6 mm and a thickness of about 0.2 mm in consideration of both the strength of a rotor shaft against an impact in the event of falling. Additionally, for the purposes of increasing inertial moment and reducing weight, radially arranged holes each having a diameter of about 5 mm are usually formed in the inertia disk.
Inertial moment I1 of a rotor provided with such an inertia disk is given, for example, by the following formula (1):I1=1.1×10−10 kgm2  (1)
Accordingly, kinetic energy E1 is given by the following formula (2):
                                                                        E                1                            =                            ⁢                                                1                  2                                ×                1.1                ×                                  10                                      -                    10                                                  ×                                                      (                                          2                      ⁢                      π                                        )                                    2                                ×                                  (                                                            5                      2                                        ~                                          10                      2                                                                                                                                              =                            ⁢                              5.4                ×                                                      10                                          -                      8                                                        ~                  2.2                                ×                                                      10                                          -                      7                                                        ⁡                                      [                    J                    ]                                                                                                          (        2        )            
On the other hand, the driving lever is made of phosphor bronze suitable for springs, and its sectional secondary moment I2 is determined by the following formula (3) on an assumption of thickness h=0.2 mm, width b=0.2 mm and length 1=0.5 mm:
                              I          2                =                                            bh              3                        12                    =                                                    0.2                ×                                  0.2                  3                                            12                        =                          1.3              ×                                                10                                      -                    4                                                  [                                  mm                  4                                                                                        (        3        )            
Also, a deflection y of a spring in a cantilevered state is expressed by the following formula (4);
                    y        =                              wl            3                                3            ⁢                          EI              2                                                          (        4        )                            where w is a spring force and E is the Young's modulus. From the above formula (4), the spring force w is determined as expressed by the following formula (5):        
                                                        w              =                            ⁢                                                y                  ×                  3                  ⁢                                      EI                    2                                                                    l                  3                                                                                                        =                            ⁢                                                0.2                  ×                  3                  ×                  10000                  ×                  1.3                  ×                                      10                                          -                      4                                                                                        5                  3                                                                                                        =                            ⁢                              6.2                ×                                                      10                                          -                      3                                                        ⁡                                      [                    kg                    ]                                                                                                          (        5        )            
Accordingly, spring energy E2 is determined by the following formula (6):
Energy efficiency η in rotating the rotor by a spring is calculated as given in the following formula (7) and η=1–4% is resulted:
                                                        η              =                            ⁢                                                                    E                    1                                                        E                    2                                                  =                                                                            (                                              0.54                        ~                        2.2                                            )                                        ×                                          10                                              -                        7                                                                                                  6.1                    ×                                          10                                              -                        6                                                                                                                                                                    =                            ⁢                              0.01                ~                0.036                                                                                        =                            ⁢                              1                ~                                  4                  ⁡                                      [                    %                    ]                                                                                                          (        7        )            
It is very difficult to output energy at such a low efficiency of not more than 5% with stability. Even a slight variation in efficiency leads to a large variation in initial speed of the gear determined by the mechanical rotating force transmitted to the same. This has raised a problem of difficulty in rotating the gear with stability.
A third object of the present invention is to provide a starter for an electromagnetic converter and a timepiece, which can improve efficiency of a startup spring for applying a mechanical rotating force to a rotor or mechanical energy transmitting means.
Moreover, another problem of the above-cited invention has been encountered in that it is difficult to correctly set the time with high accuracy because the rotational speed of the sped-up rotor does not become stable unless the rotating force applied to the gear of the wheel train is controlled by the driving lever with high accuracy.
Stated otherwise, until the IC starts driving, a time lapsed from the start of rotation of the rotor, for example, cannot be detected. For this reason, an error in setting of the correct time must be canceled by adding a preset compensation value.
However, unless the rotation of the rotor is stable, a time lapsed until the start of driving of the IC is also varied. This has raised a problem that the correct time cannot be set even with compensation using a preset value, thus resulting in a difficulty in setting the time right with high accuracy.
Further, in order to keep constant the rotating force produced by the driving lever, a deflection of the driving lever, for example, must be controlled with high accuracy. This necessity has raised still another problem that, although such a parameter can be easily managed up to accuracy enough for ordinary uses, the parameter is difficult to manage at accuracy higher than such a level.
A fourth object of the present invention is to provide a starter for an electromagnetic converter and a timepiece, which can easily stabilize a rotational speed of a rotor.